B1809 – Lamp Tail Output Circuit Short To Ground

The ODBII code B1809 indicates a short circuit in the tail lamp output circuit, meaning there is an unintended connection to ground that is affecting the tail lamp operation.

The severity of ODBII code B1809 is moderate.

Common Causes For: B1808 Lamp Tail Output Circuit Short To Battery

• Shorted wiring or connectors
• Faulty tail lamp assembly
• Damaged or corroded ground connections
• Malfunctioning body control module (BCM)
• Incorrectly installed or damaged aftermarket lighting
• Water intrusion in electrical connectors
• Frayed or pinched wires in the tail lamp circuit

Common misdiagnosis for B1809 Lamp Tail Output Circuit Short To Ground

• Faulty tail light bulb
• Bad tail light assembly
• Damaged wiring harness
• Faulty body control module (BCM)
• Poor ground connection
• Shorted wiring in the trunk or rear area
• Incorrectly installed aftermarket lighting
• Corroded connectors or terminals

Common Troubleshooting Steps

The OBD-II code B1809 indicates a problem with the tail lamp output circuit, specifically a short to ground. This code is often related to the vehicle’s body control module (BCM) and the tail lamp circuit. Here are some common troubleshooting steps to diagnose and resolve the issue:

• Visual Inspection:
• Check the wiring and connectors associated with the tail lamp circuit for any visible damage, fraying, or corrosion.
• Inspect the tail lamp assembly for any signs of water intrusion or damage.
• Check Fuses:
• Locate the fuse associated with the tail lamp circuit and check if it is blown. Replace it if necessary and see if the code returns.
• Use a Multimeter:
• With the vehicle’s ignition in the “on” position (but the engine off), use a multimeter to check for continuity in the tail lamp circuit.
• Measure the resistance between the tail lamp output circuit and ground. A very low resistance (close to 0 ohms) indicates a short to ground.
• Inspect Ground Connections:
• Check the ground connections for the tail lamp circuit. Ensure they are clean, tight, and free of corrosion.
• Check for Shorts:
• Trace the wiring from the BCM to the tail lamp assembly. Look for any areas where the wire may be pinched, chafed, or in contact with metal surfaces that could cause a short to ground.
• Test the Tail Lamp Assembly:
• Disconnect the tail lamp assembly and check the wiring harness for shorts. If the code clears with the assembly disconnected, the issue may be within the tail lamp assembly itself.
• Scan Tool Data:
• Use an OBD-II scanner to check for any additional codes that may provide more context to the issue.
• Monitor live data to see if the BCM is receiving the correct signals from the tail lamp circuit.
• Check the BCM:
• If all wiring and components appear to be in good condition, the issue may lie within the body control module itself. Testing or replacing the BCM may be necessary.
• Repair or Replace:
• Based on your findings, repair any damaged wiring or connectors. If components are faulty, replace them as needed.
• Clear Codes and Test Drive:
• After making repairs, clear the OBD-II codes and take the vehicle for a test drive to see if the code returns. If you are not comfortable performing these steps or if the issue persists, it may be best to consult a professional mechanic for further diagnosis and repair.